1. Field of the Invention
The present invention relates to an ultrasound diagnostic imaging apparatus.
2. Description of Related Art
In ultrasound diagnosis, beating of a heart and movement of a fetus can be displayed in real time by a simple operation such as applying an ultrasound probe on body surface. Since ultrasound diagnosis is a highly safe procedure, ultrasound examination can be performed repeatedly.
In such technique for displaying an ultrasound image, it is known that an image with good contrast can be obtained by visualizing harmonic components (for example, frequencies 2f0, 3f0, etc.) of fundamental wave components (frequency f0) of transmission signals. Such image capturing method is referred to as Tissue Harmonic Imaging.
Above mentioned harmonic components occur due to non-linear distortions that mainly occur when ultrasound transmits inside a subject. In other words, with respect to ultrasound which is emitted inside a living body, their signals deform while being transmitted through tissues due to their non-linear responses and the harmonic components increase. As a result, the corresponding received signals include frequency components 2f0 which are double the fundamental wave f0 and frequency components 3f0 which are triple the fundamental wave f0, for example.
Pulse inversion is known as a method to extract harmonic components in the tissue harmonic imaging. In the pulse inversion, the first and the second transmission pulse signals, one transmission pulse signal being a signal whose polarity or time is inverse of the other transmission pulse signal. Then, their received signals are combined to cancel out the fundamental wave components and emphasize the second harmonic components. Such technique is disclosed in JP 2000-300554, JP 2002-301068 and JP 2003-310609, for example.